This invention relates generally to apparatus for properly positioning and interfitting an uncured tire carcass and a tire curing bladder of a vulcanization mold relative to one another, and more particularly to so positioning an uncured tire carcass which has been at least partially toroidally pre-shaped (for example, a radial ply carcass) prior to its positioning in the mold.
Vulcanization molds for curing vehicular pneumatic tire carcasses have long been known in the art. One common type of vulcanization mold is generally referred to as a "clamshell" type mold which essentially comprises upper and lower mold half-sections and an upstanding curing bladder attached to and coaxial with the lower half-section of the mold. With such a mold, a tire carcass is prepared for curing by surrounding the mold bladder with the carcass and by placing one bead region thereof in contact with the interior of the lower half-section of the mold. The upper half-section of the mold is then lowered, initiating the conventional curing sequence.
In the case of conventional bias ply tires of the flat band type, the procedure involved is relatively direct. The uncured tire carcass, which is generally cylindrical in configuration, is positioned around the generally cylindrically shaped bladder, the axial height of which bladder has been preselected to be generally the same as the axially extending height of the cylindrically uncured tire carcass. The top half-section of the "clamshell" may, thus, be simply lowered, simultaneously forcing both the upper bead portion of the cylindrical carcass and the upper portion of the bladder downwardly as the bladder is filled with pressurized steam. Such apparatus has long been acceptable to expand the bladder smoothly and free of wrinkles into the raw tire carcass to enable the latter to be effectively cured.
The advent, however, of radial ply tires has caused substantial difficulties with the aforementioned conventional "clamshell" system. These difficulties are due primarily to the fact that the bladder is generally cylindrical and conventional radial ply tires are usually pre-shaped in the form of a generally toroidal configuration prior to the vulcanization thereof; that is, while they still are raw tire carcasses. As a result, it is difficult to fit the cylindrical bladder into the interior of the toroidally shaped carcass without wrinkling the bladder. It, thus, quickly becomes clear that such conventional apparatus utilized for vulcanizing bias ply, flat belt, cylindrical raw tire carcasses is inappropriate for vulcanizing pre-shaped tires, for example, heavy duty, steel-belted, radial ply tires.
The tire industry, in an effort to avoid the loss of its substantial capital investment in its "clamshell" molds used for curing conventional bias ply tire carcases of the flat band type, has attempted to modify such molds or the systems of which such molds are a portion so as to render them suitable for use in curing pre-shaped tire carcasses, such as radial ply tire carcasses. One example of such a modified mold system is illustrated in U.S. Pat. No. 2,997,738. This patent teaches the substitution of the aforementioned bladder extending piston by a "double-acting piston"; that is to say, by two pistons connected to the lower mold portion, one piston serving the original purpose of axially extending the bladder so as to enable the positioning thereabout of the pre-shaped uncured tire carcass, and the second piston serving to draw the uppermost portion of the bladder downwardly until it is in alignment with the uppermost bead of the tire carcass.
Although this structure appears to be operable for curing pre-shaped tire carcasses, it has certain drawbacks and disadvantages. Chief among such drawbacks is the fact that the "double-acting piston" cylinder is subject to leakage whereby water, the hydraulic medium used, seeps into the interior of the bladder and interferes with the steam in its effectiveness to uniformly vulcanize the tire carcass. Such leakage or seepage occurs principally when the "double-acting piston" is retracted to fit the bladder into the toroidally preshaped carcass.
Another disadvantage is the cost and complexity in modifying the existing "clamshell" molds by substituting "double acting pistons" for the existing "single-acting pistons".